jeffB

My 1998 Triptronic finally failed at 143,000.

I now am in the process of installing a 2001 S-8 Triptronic in my 1998 A-8. I have purchased a new harness and TCM for the S-8 tranny but have to figure out how to interface between the old engine control module and the newer Trans Control Module.

I want to stay with the older engine control module if possible and just "fool" the TCM so that it will function without going into default.

Any of you out there ever make this swap or have the solution to the interface problem that I am facing? JeffB

Paldi

Don't you need a different rear diff? Ratios different for an "S"?

jeffB

The transmission has a distributor gear that is a different ratio for the S-8 so that the rear output shaft will match the rearend ratio. All of the information that I have researched indicates that the A-8 and S-8 have the same rear end ratio when equipped with the automatic transmission.
The 6-speed manual uses a 4.11:1 rear end ratio which is different than the auto (3.7:1)

The mechanical part of the swap is straight forward. The transmission uses a different harness and updated transmison control module which I have purchased from Audi.

The interface between the old and the new electronics is where the brainstorming needs to be done. It would seem that the TCU would be easily fooled to think that it has all of the necessary information to function without default. This is what I am working on.

mclarenm8d

The intermediate gears in the S8 auto tranny "overdrive" the driveshaft to drop the 4.111 in the rear to the 3.73.

All S8's, auto or manual, have the same rear diff ring and pinion, the 37-9 combo.<ul><li><a href="https://forums.audiworld.com/a8/msgs/24154.phtml">https://forums.audiworld.com/a8/msgs/24154.phtml</a</li></ul>

mclarenm8d

There are 13 signals across the CAN Bus, you may be able to simply get the S8 TCM to work. Off hand, the issues that I can think of to verify are rev limiter effects and if the speedo reading will trip up the ECU. You will be running less MPH by RPM and gear than what your ECU is expecting, although I predict your speedo measurment will be accurate (feeds off of the half shaft).

mclarenm8d

Are you sure you need the different wiring harness and TCM? TCM to ECM should work similar across the CAN-Bus.

Now, I'll admit that I haven't seen the two sets side by side. Other than possible changes in wire colors, my thought is that they should be reasonably the same.

Please keep us up to date on your progress with this. Very interesting, and a topic others have thought about doing but haven't worked through on this forum.

jeffB

Each control unit has its own rev limiter. I have a modified chp in the engine control unit with a 7,300 rev-limit that I have never seen with the old transmission since the original tranny has the rev-limiter for transmission shifts set around 6,300.

Don't know how the ECU processes the speedo reading.

I intend to review the Bentley manual as soon as I can get mine reinstalled from Bentley.

jeffB

I completely missed the discussion forum in April where the final drive ratios were researched and spelled out for the S-8 Triptronic.

I looked up the part numbers for the rear differential and came up with the following:

2001 S-8

Part# Ratio Model
01R 500 044G 37/9 EUU

2000 S-8

01R 500 043G 37/9 DSA


1997,98, 99 S-8 4 Valve or six speed A-8

01R 500 043K 37/39 CVG/DNU


I would think that any of these would work with the S-8 Tiptronic?

Any thoughts??

PaulW

There is nothing to recode on the 97-99 ECU's. Here's info from the Bently:

-------------------------------
Engine Control Module (ECM) coding, checking

If vehicle coding information is not as specified:

- Replace ECM.

Notes:

Vehicle information is "hard coded" into the ECM. Service coding of the ECM is not possible.

Coding versions may be checked (only) using the VAG1551 or VAG1552 Scan Tool (ST).

While checking coding versions, the 5-digit ECM code must always be displayed.

- Connect VAG1551 or VAG1552 Scan Tool (ST) and press buttons -0- and -1- to insert "Engine Electronics" address word 01 (ignition switched on) Page 01-5 .

Rapid data transfer Q

01 - Engine Electronics

Indicated on display

- Press -Q- button to confirm input.

4D0907557.. 3,7L V8/4V MOTR AT D..

Coding 01153 WSC 12345

Indicated on display (ECM identification and coding)

Coding
Model
01273
A8 4.2 liter, engine code ABZ
01153
A8 3.7 liter, engine code AEW




--------------------------------------------------------------------------------

01-47


- Advance program sequence by pressing button.

Rapid data transfer HELP

Select function XX

Indicated on display

- Press buttons -0- and -6- to select "End Output" (scan tool function 06), and press -Q- button to confirm input.

------------------------------------

The 00 and newer cars have different coding, depending if the car has DSP, here are the possiblities:

USA; LEV (emission standard)
07

All-wheel drive with ESP

7

Automatic transmission

5

Audi A8

3

Code number
07 7 5 3


The "5" denotes automatic transmission, so it shouldn't matter what year tranny you have.

You can't change the coding of your ECU, so I guess it's all a mute point. Hopefully it will work!

As far as coding the tranny TCU, the only thing you can do is code it to sport, etc as found with instructions on audipages.

Good luck, keep us posted!

Paul

jeffB

I am trying to locate a 37/9 .rear differential. If you know where one is available, please let me know